1. Field of the Invention
The present invention relates to an oil type discrimination method and an oil type discriminator to execute the method used when oils of different types are transported in order or classified and stored in respective tanks, for example, in a pipeline or at an oil tank station. More particularly, the invention relates to an oil type discrimination method and an oil type discriminator that discriminate the type of oil of regular gasoline, high-octane gasoline, kerosene, and diesel oil from each other using near infrared light.
2. Description of the Related Art
As an oil type discrimination method of this kind, a discrimination method that uses sound waves and a discrimination method that uses the absorbance of a specific wavelength of ultraviolet light are known.
However, with the method that uses sound waves, it is difficult to discriminate between regular gasoline and high-octane gasoline, and there is a problem that the dependence of sound speed upon temperature. The method that uses the absorbance of a specific wavelength of ultraviolet light is less versatile because the absorbance of, for example, gasoline, differs from maker to maker and at the same time, a high-voltage power source is necessary as a power source of a light source, and therefore, it is required to install the light source away from a sensor to design for an explosion-proof structure, and thus there is a problem that the size of the discriminator becomes large.
As an oil type discrimination method capable of solving these problems, a method of measuring the absorbance of near infrared light is described in, for example, Japanese Patent Application Laid-open No. H7-294428 (for example, see claims 1 to 3).
In the oil type discrimination method described in Japanese Patent Application Laid-open No. H7-294428, the absorbance or the transmitted light output of an oil is measured using one wavelength or plural wavelengths of light in a near infrared region, and then, the absorbance or the value of transmitted light output obtained using one wavelength and subjected to operation processing, or the absorbance or the value of transmitted light output obtained using two or more wavelengths and subjected to operation processing is compared with their reference value, and thus the type of oil is discriminated.
It is desirable that the one wavelength is set to about 925 to 940 nm or about 1,210 to 1,240 nm, or two wavelengths, that is, a first wavelength of about 930 nm and a second wavelength of about 960 to 1,000 nm, or two wavelengths, that is, a first wavelength of about 1,210 nm and a second wavelength of about 1,150 to 1,200 nm, or two wavelengths, that is, a first wavelength of about 1,220 nm and a second wavelength of about 1,240 to 1,400 nm are used.
With the oil type discrimination method according to Japanese Patent Application Laid-open No. H7-294428, it is possible to discriminate between regular gasoline and high-octane gasoline and there is no influence of temperature, and further a power source and a sensor of small power type can be used, and therefore, an explosion-proof structure can be implemented comparatively easily.
However, with the discrimination method described in Japanese Patent Application Laid-open No. H7-294428, if components that shield transmitted light (hereinafter, “light-shielding components”), such as bubbles, water, and iron powder, exist in an oil, a variation is caused in the light incident to the sensor and there is a problem that the type of oil cannot be accurately discriminated.
On the other hand, in a pipeline or at an oil tank station, when the type of oil to be transported is switched to another, a state is brought about where two types of oils are mixed before and after the switching, and in this case, there is a possibility that the absorbance of the mixed oil closely resembles the absorbance of a single type of oil depending on the types of mixed oils, causing an erroneous discrimination of the type of oil.